The present invention relates to a method and apparatus for forming a mixture containing regulated, low concentration of a target component within a carrier fluid. More particularly the present invention relates such a method and apparatus in which the mixture comprises a calibration gas formed of a nitrogen carrier fluid and a moisture target component present within the mixture in minute quantities.
Mixtures having regulated, low concentrations of a specific target component have many uses in the prior art. One important application of such mixtures is in the calibration of sensitive instruments used in assuring the purity of process gases and process equipment used in the manufacture of semiconductors. An important aspect of purity assurance in semiconductor manufacturing is the virtual elimination of moisture contamination which can decrease the manufacturing yield of semiconductors. Thus, process gases used in semiconductor manufacturing as well as the processing environment for semicondutors are tested to make certain that such manufacturing is carried out in an environment essentially free of moisture. This is accomplished testing equipment well known in the art, which before use, must be calibrated. Calibration is effected by exposing the testing equipment to nitrogen gas containing variable levels of moisture in very low concentrations.
Such calibration gases, which can comprise components other than nitrogen and moisture, are manufacturing by blending and diluting high concentration mixtures with a pure diluting gas. For instance, a mixture of nitrogen and moisture having a known, high concentration can be diluted with ultra high purity nitrogen to create a mixture of nitrogen and moisture in which the moisture is present within the mixture in fractions of parts per million. Such mixtures are created by permeation devices which themselves must be individually calibrated to account for differences arising from manufacturing tolerances. As can be appreciated, their manufacturing and use is accompanied by a high degree complexity and expense.
As will be discussed, the present invention provides a method and apparatus for forming a mixture containing a carrier gas and a regulated, low concentration of a target component without the expense and complexity involved in using prior art equipment which must be calibrated to accord for manufacturing differences between individual machines. It is to be mentioned that the present invention is not limited to the formation of calibration gases and as will become apparent to those skilled in the art, the present invention could be put to other uses. However, the present invention is readily adapted to manufacture calibration mixtures, and hence, will be discussed in relation to such use.